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Bouncy Castle CVE-2026-59650

| EUVDEUVD-2026-52024 CRITICAL
Improper Input Validation (CWE-20)
2026-08-03 bcorg GHSA-ghgq-7g74-28wp
Java Information Disclosure Bc Java Bc Lts Java Red Hat
Critical
Disputed · 9.3 Vendor: bcorg
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Severity by source

Sources disagree (Medium–Critical)
Vendor (bcorg) PRIMARY
9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
vuln.today AI
7.4 HIGH

Network peer needs no auth (PR:N) but exploitation demands a static/reused key and many crafted exchanges plus CRT (AC:H); key recovery yields high confidentiality and integrity impact, no availability effect.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
7.4 HIGH
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: bcorg

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 03, 2026 - 01:31 vuln.today
Analysis Generated
Aug 03, 2026 - 01:31 vuln.today
CVE Published
Aug 03, 2026 - 00:42 cve.org
CRITICAL 9.3

DescriptionCVE.org

In Bouncy Castle for Java before 1.85, MTI/A0 DH agreement exponentiates unvalidated peer value. This issue also affects Bouncy Castle for Java LTS before 2.73.12.

Articles & Coverage 1

News Critical Private Key Recovery in Bouncy Castle for Java (bc-java) - CVE-2026-59650 Aug 03, 2026

AnalysisAI

Private key recovery in Bouncy Castle for Java (bc-java before 1.85, bc-lts-java before 2.73.12) affects the DH agreement code path, where a peer-supplied public value is exponentiated with the local private key without full range/subgroup validation. A malicious protocol peer can submit small-order or out-of-range Diffie-Hellman elements to mount a small-subgroup confinement attack and, when the local private key is static/reused, gradually recover it via CRT - enabling decryption and impersonation. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Establish DH peer session with static-key server
Delivery
Send crafted small-order/out-of-range value
Exploit
Server exponentiates unvalidated element
Execution
Repeat to leak exponent mod small factors
Persist
Reconstruct private key via CRT
Impact
Decrypt traffic or impersonate server
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Vulnerability AssessmentAI

Exploitation Exploitation requires the target to use Bouncy Castle's MTI/A0 / DHAgreement key agreement with a STATIC or REUSED DH private key - the small-subgroup confinement attack recovers the private exponent only because the same key processes many crafted peer values. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Signals are mixed and require judgement. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario A server uses Bouncy Castle's DHAgreement with a long-term (static) DH private key. A malicious client repeatedly initiates key agreements sending crafted peer values such as 1, p-1, or p, each leaking the server's private exponent modulo a small factor; the attacker then combines the residues via CRT to reconstruct the full static private key and decrypt or impersonate traffic. …
Remediation Vendor-released patch: upgrade bc-java to 1.85 or later, and bc-lts-java to 2.73.12 or later, per the advisory at https://github.com/bcgit/bc-java/wiki/CVE-2026-59650 (fix commit daeaae9d7075d04f40812e68671ebf4c777b5148); SUSE users should apply their distribution's updated Bouncy Castle package. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, inventory all systems and applications using bc-java before 1.85 or bc-lts-java before 2.73.12, prioritizing those handling encryption or key agreement functions. …

Sign in for detailed remediation steps and compensating controls.

Threat intelligence, references, and detailed analysis are available after sign-in.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Server 16.0 Affected

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CVE-2026-59650 vulnerability details – vuln.today
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